Code Division Multiple Access (CDMA) and Wideband Code Division Multiple Access (W-CDMA) are wireless communication standards. In CDMA and W-CDMA, a single frequency spectrum is shared by multiple users. In order to distinguish one wireless communication device from another, a unique code sequence is associated with each wireless communication device. The wireless communication devices may identify code sequences embedded in transmitted signal samples and identify an amount of delay incurred for the transmission of signal samples between wireless communication devices using the code sequences.
In the past, there were a number of approaches available that allowed wireless communication devices to access its code sequences. A first approach involved storing a complete code:sequence in storage elements. However, when the length of a code sequence was large, this approach required a large number of storage elements. This translated into additional cost and space requirements, which were undesirable. A second approach involved generating code sequences dynamically using a pseudo random sequence generator such as a linear feedback shift register. Although pseudo random sequence generators provided a more cost and space efficient alternative to accessing code sequences, pseudo random sequence generators of the past suffered the drawback of producing a limited number of coefficients during a time period. A typical linear feedback shift register produces only one new value during each time step. If times shifted versions are desired, several linear feedback shift registers (LFSR) needed to be implemented and started at different times. Consequently, the amount of hardware resources needed for the linear feedback shift registers increased linearly with the number of multiply and accumulate operations that are implemented in parallel.
Thus, what is needed is a method and apparatus for accessing pseudo random sequences that is efficient and cost effective.